Photoresist pattern trimming methods

ABSTRACT

Provided are methods of trimming photoresist patterns. The methods involve coating a photoresist trimming composition over a photoresist pattern, wherein the trimming composition includes a matrix polymer, a thermal acid generator and a solvent, the trimming composition being free of cross-linking agents. The coated semiconductor substrate is heated to generate an acid in the trimming composition from the thermal acid generator, thereby causing a change in polarity of the matrix polymer in a surface region of the photoresist pattern. The photoresist pattern is contacted with a developing solution to remove the surface region of the photoresist pattern. The methods find particular applicability in the formation of very fine lithographic features in the manufacture of semiconductor devices.

This application claims the benefit of priority under 35 U.S.C. §119(e)to U.S. Provisional Application No. 61/582,289, filed Dec. 31, 2011, theentire contents of which are incorporated herein by reference.

BACKGROUND

The invention relates generally to the manufacture of electronicdevices. More specifically, this invention relates to methods oftrimming photoresist patterns useful in shrink processes for theformation of fine lithographic patterns.

In the semiconductor manufacturing industry, photoresist materials areused for transferring an image to one or more underlying layers, such asmetal, semiconductor and dielectric layers, disposed on a semiconductorsubstrate, as well as to the substrate itself. To increase theintegration density of semiconductor devices and allow for the formationof structures having dimensions in the nanometer range, photoresists andphotolithography processing tools having high-resolution capabilitieshave been and continue to be developed.

Positive-tone chemically amplified photoresists are conventionally usedfor high-resolution processing. Such resists typically employ a resinhaving acid-labile leaving groups and a photoacid generator. Exposure toactinic radiation causes the acid generator to form an acid which,during post-exposure baking, causes cleavage of the acid-labile groupsin the resin. This creates a difference in solubility characteristicsbetween exposed and unexposed regions of the resist in an aqueousalkaline developer solution. Exposed regions of the resist are solublein the aqueous alkaline developer and are removed from the substratesurface, whereas unexposed regions, which are insoluble in thedeveloper, remain after development to form a positive image.

One approach to achieving nm-scale feature sizes in semiconductordevices is the use of short wavelengths of light, for example, 193 nm orless, during exposure of chemically amplified photoresists. To furtherimprove lithographic performance, immersion lithography tools have beendeveloped to effectively increase the numerical aperture (NA) of thelens of the imaging device, for example, a scanner having a KrF or ArFlight source. This is accomplished by use of a relatively highrefractive index fluid (i.e., an immersion fluid) between the lastsurface of the imaging device and the upper surface of the semiconductorwafer. The immersion fluid allows a greater amount of light to befocused into the resist layer than would occur with an air or inert gasmedium. When using water as the immersion fluid, the maximum numericalaperture can be increased, for example, from 1.2 to 1.35. With such anincrease in numerical aperture, it is possible to achieve a 40 nmhalf-pitch resolution in a single exposure process, thus allowing forimproved design shrink. This standard immersion lithography process,however, is generally not suitable for manufacture of devices requiringgreater resolution, for example, for the 32 nm and 22 nm half-pitchnodes.

Considerable effort has been made to extend the practical resolutionbeyond that achieved with standard photolithographic techniques fromboth a materials and processing standpoint. For example, multiplepatterning processes have been proposed for printing CDs and pitchesbeyond lower resolution limits of conventional lithographic tools. Onesuch multiple patterning process is self-aligned double patterning(SADP), described for example in U.S. Patent Application Pub. No.2009/0146322A1. In this process, a spacer layer is formed overpre-patterned lines. This is followed by etching to remove all spacerlayer material on horizontal surfaces of the lines and spaces, leavingbehind only material on the sidewalls of the lines. The originalpatterned lines are then etched away, leaving behind the sidewallspacers which are used as a mask for etching one or more underlyinglayers. Since there are two spacers for every line, the line density iseffectively doubled.

For multiple patterning and other lithographic processes, the printingof isolated lines and posts having a duty ratio greater than two with agood process window is essential at the lithography stage. Achieving agood process window for isolated lines and posts through directlithographic imaging is, however, extremely difficult due to poor aerialimage contrast at defocus as compared with dense lines.

There is a continuing need in the art for improved photolithographicmethods for the formation of fine patterns in electronic devicefabrication and which avoid or conspicuously ameliorate one or more ofthe foregoing problems associated with the state of the art.

SUMMARY OF THE INVENTION

In accordance with an aspect of the invention, methods of trimmingphotoresist patterns are provided. The methods comprise, in sequence:(a) providing a semiconductor substrate comprising one or more layers tobe patterned on an upper surface thereof; (b) forming a photoresistpattern on the one or more layers to be patterned, wherein thephotoresist pattern comprises a plurality of features and is formed froma chemically amplified photoresist composition, the photoresist patterncomprising a matrix polymer having acid labile groups; (c) coating aphotoresist trimming composition over the photoresist pattern, whereinthe trimming composition comprises a matrix polymer, a thermal acidgenerator and a solvent, and wherein the trimming composition is free ofcross-linking agents; (d) heating the coated semiconductor substrate togenerate an acid in the trimming composition from the thermal acidgenerator, thereby causing a change in polarity of the photoresistmatrix polymer in a surface region of the photoresist pattern; and (e)contacting the photoresist pattern with a developing solution to removethe surface region of the photoresist pattern. As a result of methods inaccordance with the invention, the process window for formation ofpatterns such as isolated lines and posts can be significantly improved.

In accordance with a further aspect of the invention, also provided areelectronic devices formed by the methods described herein.

As used herein: “g” means grams; wt % means weight percent; “nm” meansnanometer; “s” means second; “min” means minute; “Å” means Angstrom;“mol %” means mole percent; “Mw” means weight average molecular weight;“copolymer” is inclusive of polymers containing two or more differenttypes of polymerized units; “alkyl” is inclusive of linear, branched andcyclic alkyl structures; “aliphatic” is inclusive of linear, branchedand cyclic aliphatic structures; and the articles “a” and “an” areinclusive of one or more.

DESCRIPTION OF THE DRAWINGS

The present invention will be described with reference to the followingdrawing, in which like reference numerals denote like features, and inwhich:

FIG. 1A-I illustrates a process flow for forming a photolithographicpattern in accordance with the invention.

DETAILED DESCRIPTION Photoresist Trimming Compositions

The photoresist trimming compositions include a matrix polymer, athermal acid generator and a solvent, and can include optionaladditional components. When coated over a photoresist pattern formedfrom a chemically amplified photoresist composition, the photoresisttrimming compositions can provide various benefits such as controllablyreduced resist pattern dimensions and improved process window for theformation of isolated patterns such as isolated lines and posts.

The matrix polymer allows for the compositions to be coated over thephotoresist pattern in the form of a layer having a desired thickness.This will help to ensure the presence of a sufficient content of thermalacid generator for interaction with the photoresist pattern surface.

The matrix polymer should have good solubility in the developer solutionto be used in the trimming process. For example, the matrix polymer canbe soluble in an aqueous alkaline developer, preferably aqueousquaternary ammonium hydroxide solutions such as aqueoustetramethylammonium hydroxide, or in water. To minimize residue defectsoriginated from the overcoat materials, the dissolution rate of a driedlayer of the trimming composition should be greater than that of thephotoresist pattern surface region to be removed by the developersolution. The matrix polymer typically exhibits a developer dissolutionrate of 100 Å/second or higher, preferably 1000 Å/second or higher. Thematrix polymer is soluble in the solvent of the trimming composition,described herein. The matrix polymer can be chosen, for example, frompolyvinyl alcohols, polyacrylic acids, polyvinyl pyrrolidones, polyvinylamines, polyvinyl acetals, poly(meth)acrylates and combinations thereof.Preferably, the polymer contains one or more functional group chosenfrom —OH, —COOH, —SO₃H, SiOH, hydroxyl styrene, hydroxyl naphthalene,sulfonamide, hexafluoroisopropyl alcohol, anhydrates, lactones, esters,ethers, allylamine, pyrrolidones and combinations thereof.

The content of the matrix polymer in the composition will depend, forexample, on the target thickness of the layer, with a higher polymercontent being used for thicker layers. The matrix polymer is typicallypresent in the compositions in an amount of from 80 to 99 wt %, moretypically from 90 to 98 wt %, based on total solids of the trimmingcomposition. The weight average molecular weight of the polymer istypically less than 400,000, preferably from 3000 to 50,000, morepreferably from 3000 to 25,000.

Polymers useful in the overcoat compositions can be homopolymers or canbe copolymers having a plurality of distinct repeat units, for example,two, three or four distinct repeat units. The trimming compositionstypically include a single polymer, but can optionally include one ormore additional polymer. Suitable polymers and monomers for use in theovercoat compositions are commercially available and/or can readily bemade by persons skilled in the art.

The trimming compositions further include one or more thermal acidgenerator (TAG). In the case of a photoresist based on deprotectionreaction, the TAG with heat generates an acid which can cleave the bondof acid labile groups in the photoresist pattern. Preferably, thegenerated acid is a strong acid such as sulfonic acid, and can bearomatic or non-aromatic. Preferably, the generated non-aromatic acidshave at least one fluorine substituent at the alpha position of the acidgroup. Suitable TAGs can be activated at a temperature greater than 50°C., for example, greater than 70° C., greater than 90° C., greater than120° C. or greater than 150° C. Suitable TAGs are chosen from thosewhich generate aromatic or non-aromatic acids, with or without fluorinesubstitution. Examples of suitable thermal acid generators includenitrobenzyl tosylates, such as 2-nitrobenzyl tosylate, 2,4-dinitrobenzyltosylate, 2,6-dinitrobenzyl tosylate, 4-nitrobenzyl tosylate;benzenesulfonates such as 2-trifluoromethyl-6-nitrobenzyl4-chlorobenzenesulfonate, 2-trifluoromethyl-6-nitrobenzyl 4-nitrobenzenesulfonate; phenolic sulfonate esters such as phenyl,4-methoxybenzenesulfonate; alkyl ammonium salts of organic acids, suchas triethylammonium salt of 10-camphorsulfonic acid,trifluoromethylbenzenesulfonic acid, perfluorobutane sulfonic acid; andparticular onium salts. A variety of aromatic (anthracene, naphthaleneor benzene derivatives) sulfonic acid amine salts can be employed as theTAG, including those disclosed in U.S. Pat. Nos. 3,474,054, 4,200,729,4,251,665 and 5,187,019. Typically, the TAG will have a very lowvolatility at temperatures between 170 and 220° C. Examples of TAGsinclude those sold by King Industries, Norwalk, Conn. USA under NACURE™,CDX™ and K-PURE™ names, for example, NACURE 5225, CDX-2168E, K-PURE™2678 and K-PURE™ 2700. The thermally-sensitive component is typicallypresent in the composition in an amount of from about 0.1 to 20 wt %based on the total solids of the trimming composition.

Preferable thermal acid generators for use in the trimming compositionsinclude the following:

wherein M+ is an organic cation, preferably an organic cation chosenfrom the following general formulae I-IV:

wherein R₁, R₂ and R₃ are each independently chosen from hydrogen andorganic groups such as alkyl and phenyl, preferably, C1 to C5 alkyl withoptional fluorine substitution, preferable such cations including, forexample, NH₄+, CF₃CH₂NH₃+, (CH₃)₃NH+, (C₂H₅)₃NH+ and (CH₃)₂(C₂H₅)NH+;

wherein: R4 is chosen from hydrogen and organic groups such as alkyl andaryl, preferably C1 to C5 alkyl with optional fluorine substitution orphenyl; and n is an integer of from 3 to 12, preferably 5 or 6;

wherein: R₅, R₆ and R₇ are independently chosen from hydrogen andorganic groups such as alkyl and aryl, preferably C1 to C5 alkyl withoptional fluorine substitution or phenyl, preferably, at least one ofR₅, R₆ and R₇ is a non-aromatic group; and

wherein: R₈ and R₉ are independently chosen from hydrogen and organicgroups such as alkyl and aryl, preferably C1 to C5 alkyl with optionalfluorine substitution or phenyl, preferably, at least one of R₈ and R₉is a non-aromatic group.

The trimming compositions further include a solvent or solvent mixture.Suitable solvent materials to formulate and cast the trimmingcompositions exhibit excellent solubility characteristics with respectto the non-solvent components of the trimming composition, but do notappreciably dissolve the underlying photoresist pattern so as tominimize intermixing. The solvent is typically chosen from water,organic solvents and mixtures thereof. Suitable organic solvents for theovercoat composition include, for example: alkyl esters such as alkylpropionates such as n-butyl propionate, n-pentyl propionate, n-hexylpropionate and n-heptyl propionate, and alkyl butyrates such as n-butylbutyrate, isobutyl butyrate and isobutyl isobutyrate; ketones such as2,5-dimethyl-4-hexanone and 2,6-dimethyl-4-heptanone; aliphatichydrocarbons such as n-heptane, n-nonane, n-octane, n-decane,2-methylheptane, 3-methylheptane, 3,3-dimethylhexane and2,3,4-trimethylpentane, and fluorinated aliphatic hydrocarbons such asperfluoroheptane; and alcohols such as straight, branched or cyclicC₄-C₉ monohydric alcohol such as 1-butanol, 2-butanol,3-methyl-1-butanol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol,2-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 2-hexanol, 2-heptanol,2-octanol, 3-hexanol, 3-heptanol, 3-octanol and 4-octanol;2,2,3,3,4,4-hexafluoro-1-butanol, 2,2,3,3,4,4,5,5-octafluoro-1-pentanoland 2,2,3,3,4,4,5,5,6,6-decafluoro-1-hexanol, and C₅-C₉ fluorinateddiols such as 2,2,3,3,4,4-hexafluoro-1,5-pentanediol,2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediol and2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoro-1,8-octanediol; and mixturescontaining one or more of these solvents. Of these organic solvents,alcohols, aliphatic hydrocarbons and ethers are preferred. The solventcomponent of the trimming composition is typically present in an amountof from 90 to 99 wt % based on the trimming composition.

The trimming compositions may include optional additives. For example,to allow for development with an organic solvent developer, the trimmingcomposition can include an additional component that reacts with thesurface region of the resist pattern, rendering it soluble in theorganic solvent developer. This component preferably contains functionalgroups chosen from —OH, —NH, —SH, ketones, aldehydes, —SiX wherein X isa halogen, vinyl ethers and combinations thereof. Such a component isparticularly useful for negative tone development (NTD) processes. Thecomponent diffuses into the surface region of the NTD photoresist andreacts with carboxylic acid groups at the resist surface. This reactionresults in a polarity change of the surface, rendering the surfacesoluble in the organic solvent developer, for example, 2-heptanone orn-butyl acetate. Such component if used is typically present in anamount of from 0.1 to 10 wt % based on total solids of the trimmingcomposition.

The trimming composition can further include a surfactant. Typicalsurfactants include those which exhibit an amphiphilic nature, meaningthat they can be both hydrophilic and hydrophobic at the same time.Amphiphilic surfactants possess a hydrophilic head group or groups,which have a strong affinity for water and a long hydrophobic tail,which is organophilic and repels water. Suitable surfactants can beionic (i.e., anionic, cationic) or nonionic. Further examples ofsurfactants include silicone surfactants, poly(alkylene oxide)surfactants, and fluorochemical surfactants. Suitable non-ionicsurfactants include, but are not limited to, octyl and nonyl phenolethoxylates such as TRITON® X-114, X-100, X-45, X-15 and branchedsecondary alcohol ethoxylates such as TERGITOL™ TMN-6 (The Dow ChemicalCompany, Midland, Mich. USA). Still further exemplary surfactantsinclude alcohol (primary and secondary) ethoxylates, amine ethoxylates,glucosides, glucamine, polyethylene glycols, poly(ethyleneglycol-co-propylene glycol), or other surfactants disclosed inMcCutcheon's Emulsifiers and Detergents, North American Edition for theYear 2000 published by Manufacturers Confectioners Publishing Co. ofGlen Rock, N.J. Nonionic surfactants that are acetylenic diolderivatives also can be suitable. Such surfactants are commerciallyavailable from Air Products and Chemicals, Inc. of Allentown, Pa. andsold under the trade names of SURFYNOL® and DYNOL®. Additional suitablesurfactants include other polymeric compounds such as the tri-blockEO-PO-EO co-polymers PLURONIC® 25R2, L121, L123, L31, L81, L101 and P123(BASF, Inc.). Such surfactant and other optional additives if used aretypically present in the composition in minor amounts such as from 0.01to 10 wt % based on total solids of the trimming composition.

The trimming compositions are free of cross-linking agents as suchmaterials can result in a dimensional increase of the resist pattern.Typically, the trimming compositions are free of basic quenchers andbase generators, for example, thermal base generator compounds, as suchcompounds may neutralize the effects of the thermal acid generatorcomponent in the trimming compositions. However, it may be useful toinclude a basic material such as an amine or amide in certain instances,for example, when using an onium salt TAG. In such case, the basicmaterial may be useful for adjusting the thermal acid generationtemperature.

The photoresist trimming compositions can be prepared following knownprocedures. For example, the compositions can be prepared by dissolvingsolid components of the composition in the solvent components. Thedesired total solids content of the compositions will depend on factorssuch as the desired final layer thickness. Preferably, the solidscontent of the trimming compositions is from 1 to 10 wt %, morepreferably from 1 to 5 wt %, based on the total weight of thecomposition.

Photoresist Pattern Trimming Methods

Processes in accordance with the invention will now be described withreference to FIG. 1A-I, which illustrates an exemplary process flow forforming a photolithographic pattern using a photoresist pattern trimmingtechnique. While the illustrated process flow is of a positive tonedevelopment process for forming the resist pattern, the invention isalso applicable to a pattern formed by negative tone development (NTD).

FIG. 1A depicts in cross-section a substrate 100 which may includevarious layers and features. The substrate can be of a material such asa semiconductor, such as silicon or a compound semiconductor (e.g.,III-V or II-VI), glass, quartz, ceramic, copper and the like. Typically,the substrate is a semiconductor wafer, such as single crystal siliconor compound semiconductor wafer, and may have one or more layers andpatterned features formed on a surface thereof. One or more layers to bepatterned 102 may be provided over the substrate 100. Optionally, theunderlying base substrate material itself may be patterned, for example,when it is desired to form trenches in the substrate material. In thecase of patterning the base substrate material itself, the pattern shallbe considered to be formed in a layer of the substrate.

The layers may include, for example, one or more conductive layers suchas layers of aluminum, copper, molybdenum, tantalum, titanium, tungsten,alloys, nitrides or silicides of such metals, doped amorphous silicon ordoped polysilicon, one or more dielectric layers such as layers ofsilicon oxide, silicon nitride, silicon oxynitride, or metal oxides,semiconductor layers, such as single-crystal silicon, and combinationsthereof. The layers to be etched can be formed by various techniques,for example, chemical vapor deposition (CVD) such as plasma-enhancedCVD, low-pressure CVD or epitaxial growth, physical vapor deposition(PVD) such as sputtering or evaporation, or electroplating. Theparticular thickness of the one or more layers to be etched 102 willvary depending on the materials and particular devices being formed.

Depending on the particular layers to be etched, film thicknesses andphotolithographic materials and process to be used, it may be desired todispose over the layers 102 a hard mask layer 103 and/or a bottomantireflective coating (BARC) 104 over which a photoresist layer 106 isto be coated. Use of a hard mask layer may be desired, for example, withvery thin resist layers, where the layers to be etched require asignificant etching depth, and/or where the particular etchant has poorresist selectivity. Where a hard mask layer is used, the resist patternsto be formed can be transferred to the hard mask layer 103 which, inturn, can be used as a mask for etching the underlying layers 102.Suitable hard mask materials and formation methods are known in the art.Typical materials include, for example, tungsten, titanium, titaniumnitride, titanium oxide, zirconium oxide, aluminum oxide, aluminumoxynitride, hafnium oxide, amorphous carbon, silicon oxynitride andsilicon nitride. The hard mask layer can include a single layer or aplurality of layers of different materials. The hard mask layer can beformed, for example, by chemical or physical vapor depositiontechniques.

A bottom antireflective coating may be desirable where the substrateand/or underlying layers would otherwise reflect a significant amount ofincident radiation during photoresist exposure such that the quality ofthe formed pattern would be adversely affected. Such coatings canimprove depth-of-focus, exposure latitude, linewidth uniformity and CDcontrol. Antireflective coatings are typically used where the resist isexposed to deep ultraviolet light (300 nm or less), for example, KrFexcimer laser light (248 nm) or ArF excimer laser light (193 nm). Theantireflective coating can comprise a single layer or a plurality ofdifferent layers. Suitable antireflective materials and methods offormation are known in the art. Antireflective materials arecommercially available, for example, those sold under the AR™ trademarkby Rohm and Haas Electronic Materials LLC (Marlborough, Mass. USA), suchas AR™40A and AR™124 antireflectant materials.

A photoresist layer 106 formed from a chemically amplifiedphotosensitive composition comprising a matrix polymer having acidlabile groups is disposed on the substrate over the antireflective layer(if present). The photoresist composition can be applied to thesubstrate by spin-coating, dipping, roller-coating or other conventionalcoating technique. Of these, spin-coating is typical. For spin-coating,the solids content of the coating solution can be adjusted to provide adesired film thickness based upon the specific coating equipmentutilized, the viscosity of the solution, the speed of the coating tooland the amount of time allowed for spinning. A typical thickness for thephotoresist layer 106 is from about 500 to 3000 Å.

The photoresist layer 106 can next be softbaked to minimize the solventcontent in the layer, thereby forming a tack-free coating and improvingadhesion of the layer to the substrate. The softbake can be conducted ona hotplate or in an oven, with a hotplate being typical. The softbaketemperature and time will depend, for example, on the particularmaterial of the photoresist and thickness. Typical softbakes areconducted at a temperature of from about 90 to 150° C., and a time offrom about 30 to 90 seconds.

The photoresist layer 106 is next exposed to activating radiation 108through a first photomask 110 to create a difference in solubilitybetween exposed and unexposed regions. References herein to exposing aphotoresist composition to radiation that is activating for thecomposition indicates that the radiation is capable of forming a latentimage in the photoresist composition. The photomask has opticallytransparent and optically opaque regions 112, 114 corresponding toregions of the resist layer to be exposed and unexposed, respectively,by the activating radiation. The exposure wavelength is typicallysub-400 nm, sub-300 nm or sub-200 nm such as 193 nm or EUV wavelengths,with 248 nm and 193 nm being typical. The exposure energy is typicallyfrom about 10 to 80 mJ/cm², dependent upon the exposure tool and thecomponents of the photosensitive composition.

Following exposure of the photoresist layer 106, a post-exposure bake(PEB) is performed. The PEB can be conducted, for example, on a hotplateor in an oven. Conditions for the PEB will depend, for example, on theparticular photoresist composition and layer thickness. The PEB istypically conducted at a temperature of from about 80 to 150° C., and atime of from about 30 to 90 seconds. A latent image defined by theboundary between polarity-switched and unswitched regions (correspondingto exposed and unexposed regions, respectively) is thereby formed.

The photoresist layer is next developed to remove exposed regions of thephotoresist layer 106, leaving unexposed regions forming a resistpattern 106′ having a plurality of features as shown in FIG. 1B. Thefeatures are not limited and can include, for example, a plurality oflines and/or cylindrical posts which will allow for the formation ofline and/or contact hole patterns in the underlying layers to bepatterned. The developer is typically an aqueous alkaline developer, forexample, a quaternary ammonium hydroxide solution, for example, atetra-alkyl ammonium hydroxide solutions such as 0.26 Normality (N)(2.38 wt %) tetramethylammonium hydroxide (TMAH). In the case of anegative tone development process, where unexposed regions of thephotoresist layer are removed and exposed regions remain to form thepattern, an organic solvent developer is employed. The organic developercan, for example, be a solvent chosen from ketones, esters, ethers,hydrocarbons, and mixtures thereof. Of these, 2-heptanone and n-butylacetate are typical.

It is typical that the resist pattern, for example, the plurality oflines and/or posts have a duty ratio of 1:2 or more, 1:1.5 or more or1:1 or more before trimming. In the case of lines and posts, duty ratiois defined as the ratio of linewidth or post diameter (L) to the spacelength (S) between adjacent lines or posts, respectively (i.e., L:S). Ahigher duty ratio refers to a higher density of lines or posts, while alower duty ratio refers to a lower density of (i.e., more isolated)lines or posts. With reference to FIG. 1B, the duty ratio prior totrimming is L₁:S₁.

A layer 116 of a photoresist pattern trimming composition as describedherein is formed over the photoresist pattern 106′ as shown in FIG. 1C.The trimming composition is typically applied to the substrate byspin-coating. The solids content of the coating solution can be adjustedto provide a desired film thickness based upon the specific coatingequipment utilized, the viscosity of the solution, the speed of thecoating tool and the amount of time allowed for spinning. A typicalthickness for the pattern trimming layer 116 is from 200 to 1500 Å.

As shown in FIG. 1D, the substrate is next baked to remove solvent inthe trimming layer, to cause acid generation by the TAG, to diffuse thegenerated acid into the surface of the underlying resist pattern 106′and to allow the polarity-changing reaction in the resist patternsurface region 118. The bake can be conducted on a hotplate or in anoven 120, with a hotplate being typical. Suitable bake temperatures aregreater than 50° C., for example, greater than 70° C., greater than 90°C., greater than 120° C. or greater than 150° C., with a temperature offrom 70 to 160° C. and a time of from about 30 to 90 seconds beingtypical. While a single baking step is typical, multiple-step baking canbe used and may be useful for resist profile adjustment.

The photoresist pattern is next contacted with a developing solution toremove the trimming composition layer 116 and the surface region of thephotoresist pattern 118, with the resulting trimmed pattern being shownin FIG. 1E. The developer is typically an aqueous alkaline developer,for example, a quaternary ammonium hydroxide solution, for example, atetra-alkyl ammonium hydroxide solutions such as 0.26 Normality (N)(2.38 wt %) tetramethylammonium hydroxide (TMAH). Alternatively, anorganic solvent developer can be used, for example, a solvent chosenfrom ketones, esters, ethers, hydrocarbons, and mixtures thereof. Of theorganic solvent developers, 2-heptanone and n-butyl acetate are typical.

The duty ratio of the resist pattern after trimming (L₂:S₂) is typically1:2 or less, 1:3 or less or 1:4 or less. In the case of a doublepatterning process, a typical duty ratio is about 1:1 before trimmingand about 1:3 after trimming.

A spacer layer is next formed over the trimmed photoresist pattern andthe upper surface of the substrate using known techniques. The spacerlayer is typically formed of a material chosen from silicon nitrides,silicon oxides and silicon oxynitrides. Such materials can be depositedby various techniques, with chemical vapor deposition (CVD) such asplasma enhanced CVD being typical. This is followed by etching to removeall spacer layer material on horizontal surfaces of the lines andspaces, leaving behind spacers 120 on sidewalls of the photoresistpattern, as shown in FIG. 1F.

The first photoresist pattern 106″ is next removed, leaving behindspacers 120, as shown in FIG. 1G. Because the spacers are typicallyformed on all side surfaces of the first resist pattern with the resistpattern at the center, they generally result in a closed-ring structure.Therefore, in the case of fabricating a line pattern using the spacer, atrimming process may be performed to remove ends of the patterns toseparate the spacer into a discrete line pattern. The trimming processcan be conducted, for example, using known etching techniques.

The BARC layer 104, if present, is selectively etched using the spacers120 as an etch mask, exposing the underlying hardmask layer 103. Thehardmask layer is next selectively etched, again using the spacers 120as an etch mask, resulting in patterned BARC and hardmask layers 104′,103′, as shown in FIG. 1H. Suitable etching techniques and chemistriesfor etching the BARC layer and hardmask layer are known in the art andwill depend, for example, on the particular materials of these layers.Dry-etching processes such as reactive ion etching are typical. Thespacers 120 and patterned BARC layer 104′ are next removed from thesubstrate using known techniques.

Using the hardmask pattern 103′ as an etch mask, the one or more layers102 are selectively etched. Suitable etching techniques and chemistriesfor etching the underlying layers 102 are known in the art, withdry-etching processes such as reactive ion etching being typical. Thepatterned hardmask layer can next be removed from the substrate surfaceusing known techniques, for example, a dry-etching process such asreactive ion etching. The resulting structure is a pattern of etchedfeatures, for example, line and/or contact hole patterns. In analternative exemplary method, it may be desirable to pattern the layers102 directly without the use of a hardmask layer. Whether directpatterning is employed will depend on factors such as the materialsinvolved, resist selectivity, resist pattern thickness and patterndimensions.

The following non-limiting examples are illustrative of the invention.

EXAMPLES Photoresist Compositions

Photoresist A: A positive chemically amplified photoresist compositionwas prepared by combining: 1.35 g Polymer A (M1/M2/M3=4/4/2 mole ratio,Mw=10K) and 1.35 g Polymer B (M1/M2/M3/M4=30/35/15/20, Mw=6K), whereinthe monomer units M1-M4 are as follows:

0.51 g tri-phenyl sulfonium4-(3-hydroxy-adamantane-1-carbonyloxy)-1,1,2,2-tetrafluorobutanesulfonate (TPS-ADOH-TFBS) photoacid generator, 0.07 gtrihydroxymethyl-carbamic acid tert-butyl ester base quencher, 0.001 gPOLYFOX™ 656 surfactant, 19.34 g propylene glycol methyl ether acetateand 77.36 g methyl-2-hydroxy-iso-butyrate.Photoresist Trimming Compositions

Example 1 PTC 1

2.813 g copolymer of t-butyl acrylate/methacrylic acid (7/3 of moleratio), 0.087 g of TAG 1, 19.420 g decane and 77.680 g2-methyl-1-butynol were mixed until all components were dissolved. Theresulting mixture was filtered with a 0.2 micron Nylon filter.

Example 2 PTC 2

2.610 g of copolymer of t-butyl acrylate/methacrylic acid (7/3 of moleratio), 0.290 g of TAG 2, 24.275 g decane and 72.825 g2-methyl-1-butynol were mixed until all components were dissolved. Theresulting mixture was filtered with a 0.2 micron Nylon filter.

Lithographic Processing

Example 3

Photoresist A was spin-coated on an organic bottom antireflectivecoating (BARC AR™124 23 nm/AR™26N 77 nm (Rohm and Haas ElectronicMaterials LLC)) over 12 inch silicon wafers and softbaked (SB) at 95° C.for 60 seconds, to a thickness of 700 Å. Opticoat™ OC2000 topcoatmaterial (Rohm and Haas Electronic Materials LLC) was coated on theresist to form an immersion topcoat layer. The coated wafers wereexposed with an ASML ArF 1900i immersion scanner with NA=1.35, Dipole35Y illumination (0.9/0.635sigma), plus x polarization, andpost-exposure baked (PEB) at 90° C. for 60 seconds. The coated waferswere treated with 0.26N (normal) aqueous tetramethylammonium hydroxidesolution to develop the imaged resist layers to form 45 nm 1:1 line andspace resist patterns. Linewidth was measured for one of the patternedwafers. A 70 nm thick layer of the trimming composition of Example 1(PTC 1) or Example 2 (PTC 2) was spin-coated over another of thepatterned wafers, baked at the conditions shown in Table 1, anddeveloped in 2.38% TMAH developer for 12 seconds with a TEL Lithus GPnozzle. Linewidth measurements were made, with the results being shownin Table 1. Also measured for PCT 2 samples were effective sensitivity(ES), critical dimension (CD) and depth of focus (DOF), with the resultsbeing shown in Table 2. ES is expressed as the amount of exposure atwhich the line and space patterns reached the target CD after exposureand development.

Example 4 (Comparative)

The procedures of Example 3 were repeated, except no trimmingcomposition was coated over the wafers, and the resist-patterned waferswere developed with 2.38% TMAH for 60 seconds after the trim-bake.Linewidth measurements of the resist patterns were made before thetrim-bake and after the trim-bake/development steps, with the resultsbeing shown in Table 1.

TABLE 1 Linewidth Without Linewidth Trimming; With Linewidth WithLinewidth Trim-Bake/ With Trimming Trim-Bake Without Develop OnlyTrimming (Ex. 3/ Conditions Trimming (Comp Ex. 4) (Ex. 3/PTC 1) PTC 2)140° C./60 s 56 nm 54 nm 50 nm 48 nm 145° C./60 s 56 nm 56 nm 44 nm

TABLE 2 Linewidth Without Linewidth With Trimming Trimming (Ex. 3/PTC 2@ 145° C./60 s) Es (mJ/cm²) 67.5 39 CD (nm) 28 28 DOF (nm) 60 90The results indicate that the resist trimming compositions of theinvention are effective to shrink CDs of photoresist patterns and toenhance depth of focus.

What is claimed is:
 1. A method of trimming a photoresist pattern,comprising, in sequence: (a) providing a semiconductor substratecomprising one or more layers to be patterned on an upper surfacethereof; (b) forming a photoresist pattern on the one or more layers tobe patterned, wherein the photoresist pattern comprises a plurality offeatures and is formed from a chemically amplified photoresistcomposition, the photoresist pattern comprising a matrix polymer havingacid labile groups; (c) coating a photoresist trimming composition overthe photoresist pattern, wherein the trimming composition comprises amatrix polymer, a thermal acid generator and a solvent, and wherein thetrimming composition is free of cross-linking agents; (d) heating thecoated semiconductor substrate to generate an acid in the trimmingcomposition from the thermal acid generator, thereby causing a change inpolarity of the photoresist matrix polymer in a surface region of thephotoresist pattern; and (e) contacting the photoresist pattern with adeveloping solution to remove the surface region of the photoresistpattern.
 2. The method of claim 1, wherein the solvent of thephotoresist trimming composition is chosen from water, organic solventsand mixtures thereof.
 3. The method of claim 1, wherein the matrixpolymer of the photoresist trimming composition is soluble in aqueousalkaline developer.
 4. The method of claim 1, wherein the developingsolution is an aqueous tetramethylammonium hydroxide solution.
 5. Themethod of claim 1, wherein the matrix polymer of the photoresisttrimming composition contains functional groups selected from —OH,—COOH, —SO₃H, —SiOH, hydroxyl styrene, hydroxyl naphthalene,sulfonamide, hexafluoroisopropyl alcohol, anhydrate, lactone, ester,ether, allylamine, pyrolidone.
 6. The method of claim 1, wherein thetrimming composition further comprises a compound comprising functionalgroups chosen from —OH, —NH, —SH, ketones, aldehydes, —SiX wherein X ischosen from halogens, vinyl ethers and combinations thereof, andcombinations thereof.
 7. The method of claim 1, wherein the plurality offeatures of the photoresist pattern comprise a plurality of lines orposts having a duty ratio of 1:1 or more before trimming and 1:3 or lesssense after trimming.
 8. The method of claim 1, further comprising: (f)forming sidewall spacers on the trimmed photoresist pattern aftercontacting the photoresist pattern with the developing solution; and (g)removing the trimmed photoresist pattern, leaving sidewall spacers onthe one or more layers to be patterned.
 9. The method of claim 1,wherein the acid generated by the thermal acid generator isfluorine-substituted.
 10. The method of claim 9, wherein the solvent ofthe photoresist trimming composition is chosen from alkanes, alcohols,ethers, esters, ketones and mixtures thereof.
 11. The method of claim 1,wherein the thermal acid generator generates an aromatic acid.
 12. Themethod of claim 11, wherein the thermal acid generator is chosen fromone or more of the following compounds:

wherein M+ is an organic cation.
 13. The method of claim 1, wherein thethermal acid generator generates a non-aromatic acid.
 14. The method ofclaim 13, wherein the thermal acid generator is chosen from one or moreof the following thermal acid generators:

wherein M+ is an organic cation.
 15. The method of claim 13, wherein thenon-aromatic acid has at least one fluorine substituent at the alphaposition of the acid group.
 16. The method of claim 1, wherein thethermal acid generator generates a sulfonic acid.
 17. The method ofclaim 16, wherein the thermal acid generator is chosen from one or moreof: CF₃SO₃-M+, C₄F₉SO₃-M+, CH₃CH₂CF₂CF₂SO₃-M+ and HOCH₂CH₂CF₂CF₂SO₃-M+,wherein M+ is an organic cation.
 18. The method of claim 16, wherein thethermal acid generator is chosen from one or more of the followingthermal acid generators:

wherein M+ is an organic cation.